MPO Peroxidation Assay Kit

Transcription

1 MPO Peroxidation Assay Kit Catalog Number KA assays Version: 03 Intended for research use only

2 Table of Contents Introduction... 3 Background... 3 Principle of the Assay... 3 General Information... 4 Materials Supplied... 4 Storage Instruction... 4 Materials Required but Not Supplied... 4 Precautions for Use... 5 Assay Protocol... 6 Reagent Preparation... 6 Sample Preparation... 7 Assay Procedure... 7 Data Analysis... 9 Calculation of Results... 9 Performance Characteristics Resources Trouble shooting References Plate Layout KA / 14

3 Introduction Background Myeloperoxidase (MPO) is a member of the heme peroxidase superfamily and is stored within the azurophilic granules of leukocytes. 1 MPO is found within circulating neutrophils, monocytes, and some tissue macrophages. 2 A unique activity of MPO is its ability to use chloride as a cosubstrate with hydrogen peroxide to generate chlorinating oxidants such as hypochlorous acid, a potent antimicrobial agent. 3 Recently, evidence has emerged that MPO-derived oxidants contribute to tissue damage and the initiation and propagation of acute and chronic vascular inflammatory diseases. 4,5 The fact that circulating levels of MPO have been shown to predict risks for major adverse cardiac events and that levels of MPO-derived chlorinated compounds are specific biomarkers for disease progression, has attracted considerable interest in the development of therapeutically useful MPO inhibitors. 6 MPO also oxidizes a variety of substrates, including phenols and anilines, via the classic peroxidation cycle. The relative concentrations of chloride and the reducing substrate determine whether MPO uses hydrogen peroxide for chlorination or peroxidation. Principle of the Assay MPO Peroxidation Assay provides a convenient fluorescence-based method for detecting the MPO peroxidase activity in both crude cell lysates and purified enzyme preparations. The assay utilizes the peroxidase component of MPO. The reaction between hydrogen peroxide and ADHP (10-acetyl-3,7-dihydroxyphenoxazine) produces the highly fluorescent compound resorufin (See Figure 1). Resorufin fluorescence can be easily analyzed with an excitation wavelength of nm and emission wavelength of nm. The kit includes a MPO-specific inhibitor for distinguishing between MPO activity from MPO-independent fluorescence. KA / 14

4 General Information Materials Supplied List of component Item MPO Assay Buffer MPO Peroxidation Substrate Myeloperoxidase Control MPO Inhibitor MPO Hydrogen Peroxide MPO Resorufin MPO DMSO 96-Well Plate (black) 96-Well Cover Sheets Quantity 1 vial 5 vials 1 vial 1 vial 1 vial 1 vial 1 vial 2 plates 2 covers Storage Instruction Remove the Myeloperoxidase Control from the kit and store at -20 C. The rest of the components should be stored at 4 C. This kit will perform as specified if used before the expiration date indicated on the outside of the box. Item Storage MPO Assay Buffer 4 C MPO Peroxidation Substrate 4 C Myeloperoxidase Control -20 C MPO Inhibitor 4 C MPO Hydrogen Peroxide 4 C MPO Resorufin 4 C MPO DMSO 4 C 96-Well Plate (black) Room temperature 96-Well Cover Sheets Room temperature Materials Required but Not Supplied A fluorometer with the capacity to measure fluorescence using an excitation wavelength of nm and an emission wavelength of nm Adjustable pipettes and a repeat pipettor A source of pure water; glass distilled water or HPLC-grade water is acceptable KA / 14

5 Precautions for Use WARNING: This product is for laboratory research use only: not for administration to humans. Not for human or veterinary diagnostic or therapeutic use. Pipetting Hints It is recommended that a repeating pipettor be used to deliver reagents to the wells. This saves time and helps to maintain more precise incubation times. Before pipetting each reagent, equilibrate the pipette tip in that reagent (i.e., slowly fill the tip and gently expel the contents, repeat several times). Do not expose the pipette tip to the reagent(s) already in the well. General Information The final volume of the assay is 110 µl in all the wells. All reagents except the enzymes must be equilibrated to room temperature before beginning the assay. It is not necessary to use all the wells on the plate at one time. We recommend assaying samples in triplicate, but it is the user s discretion to do so. The assay is performed at room temperature. Monitor the fluorescence with an excitation wavelength of nm and an emission wavelength of nm. KA / 14

6 Assay Protocol Reagent Preparation MPO Assay Buffer - The vial contains 50 ml of 1X phosphate-buffered saline (PBS), ph 7.4. It is ready to use in the assay. MPO Peroxidation Substrate - Each vial contains a clear lyophilized powder of ADHP (10-acetyl-3,7-dihydroxyphenoxazine). Immediately prior to preparing the Working Solution, dissolve the contents of one vial with 100 µl of MPO DMSO and then add 400 µl of Assay Buffer for a final concentration of 1 mm. This is enough substrate to assay 100 wells. Prepare additional vials as needed. The reconstituted substrate is stable for 30 minutes. After 30 minutes, increased background fluorescence will occur. Myeloperoxidase Control - The vial contains 50 µl of a 100 µg/ml solution of human polymorphonuclear leukocyte MPO. Thaw and store the enzyme on ice while preparing the reagents for the assay. Prior to assaying, dilute 10 µl of MPO with 3.99 ml of Assay Buffer for a final MPO concentration of 250 ng/ml. The diluted enzyme is stable for one hour on ice. MPO Inhibitor - The vial contains 300 µl of 50 mm 4-aminobenzhydrazide, a MPO inhibitor. 8,9 Prior to assaying, dilute 10 µl of inhibitor with 490 µl of Assay Buffer. This is enough inhibitor to assay 50 wells. The diluted inhibitor is stable for four hours. MPO Hydrogen Peroxide - The vial contains 100 µl of a 30% solution of hydrogen peroxide. Prior to assaying, dilute 10 µl with 90 µl of Assay Buffer to yield a 3% solution. Then prepare a 5 mm solution by diluting 10 µl of the 3% solution with 1.74 ml of Assay Buffer. The 5 mm solution will be used to prepare the Working Solution. The diluted solutions are stable for two hours. MPO Resorufin - The vial contains 200 µl of a 2 mm solution of resorufin. The reagent is ready to use to prepare the resorufin standard curve. MPO DMSO - The vial contains 1 ml of dimethylsulfoxide (DMSO). The reagent is ready to use as supplied. Preparation Dilute 50 µl of the Resorufin standard with 1.95 ml of assay buffer to yield a concentration of 50 µm. Take eight clean glass test tubes and mark them A-H. Add the amount of resorufin standard (50 µm) and assay buffer to each tube as described in Table 1. The diluted standards are stable for four hours at room temperature. KA / 14

7 Tube 50 µm Resorufin (µl) Assay Buffer (µl) Final Concentration (µm) A 0 1,000 0 B C D E F G H Tabel 1. Preparation of the Resorufin standards Sample Preparation The kit is designed for detection of MPO activity in cell lysates and in purified solutions. This assay is not applicable for use with serum samples. Many reagents interfere with the peroxidation assay. Before collecting cells, check the interference section for reagents that will not interfere with the assay. Cell Lysate 1. Collect cells (~7 x 10 6 ) by centrifugation (i.e., 1,000-2,000 x g for 10 minutes at 4 C). For adherent cells, do not harvest using proteolytic enzymes; rather use a rubber policeman. 2. Sonicate cell pellet in ml of cold 1X PBS, ph 7.4, on ice. 3. Centrifuge at 10,000 x g for 10 minutes at 4 C. 4. Remove the supernatant and store on ice. 5. We recommend assaying for MPO activity on the same day of collection. If this is not possible, freeze the sample at -80 C. The sample will be stable for at least one week. Assay Procedure 1. Wells - add 60 µl of assay buffer and 50 µl of standard (tubes A-H) per well in the designated wells on the plate (see Plate layout). 2. Read the plate after five minutes in a fluorometer using an excitation wavelength of nm and an emission wavelength of nm. This will allow you to establish an appropriate GAIN for detecting the entire range of the standards. This GAIN will then be used when assaying the samples. 3. In a suitable tube, prepare the Working Solution according to the table below:. Reagents 50 wells 100 wells 150 wells 200 wells Assay Buffer 2.24 ml 4.48 ml 6.72 ml 8.96 ml Peroxidation Substrate (1 mm) 250 µl 500 µl 750 µl 1 ml Hydrogen Peroxide (5 mm) 10 µl 20 µl 30 µl 40 µl Table 2. Working Solution Preparation KA / 14

8 4. MPO Positive Control Wells - add 10 µl of assay buffer and 50 µl of 250 ng/ml MPO to two wells. 5. Sample Wells - add 10 µl of assay buffer and 50 µl of sample to two wells. To obtain reproducible results, the amount of myeloperoxidase added to the wells should fall within the range of the assay. When necessary, samples should be diluted with assay buffer or concentrated with an Amicon centrifuge concentrator with a molecular weight cut-off of 30,000 to bring the enzymatic activity to this level. 6. Inhibitor Wells - add 10 µl of diluted MPO inhibitor and 50 µl of sample to two wells. 7. Initiate the reactions by quickly adding 50 µl of the Working Solution to the positive control, sample, and inhibitor wells only. 8. Read the plate in a fluorometer every 30 seconds for 15 minutes using an excitation wavelength of nm and emission wavelength of nm. Well Type Assay Buffer MPO (250 ng/ml) Sample MPO Inhibitor Working Solution Positive Control 10 µl 50 µl µl Sample 10 µl - 50 µl - 50 µl Inhibitor µl 10 µl 50 µl Table 3. Pipetting summary KA / 14

9 Data Analysis Calculation of Results Plot the Curve 1. Determine the average fluorescence of the standards. Subtract the fluorescence value of the standard A from itself and all other standards. This is the corrected fluorescence. 2. Plot the corrected fluorescence values (from step 1 above) of each standard as a function of the final concentration of resorufin from Table 1. See Figure 2, for a typical standard curve. Determine MPO Activity 1. Determine the average fluorescence of each sample and sample plus inhibitor. 2. Determine the change in fluorescence (RFU) per minute for the sample and sample plus inhibitor by: a. Plotting the fluorescence values as a function of time to obtain the slope (rate) of the linear portion of the curve. An example of human myeloid leukemia HL60 10,000 x g supernatant assayed with and without MPO inhibitor over time is shown in Figure 3, OR b. Select two points on the linear portion of the curve and determine the change in fluorescence during that time using the following equation: RFU/min =.. 3. Calculate the MPO activity using the equation. One unit is defined as the amount of enzyme that will cause the formation of 1 nmol of fluorophore per minute at 25 C. MPO Peroxidase Activity (nmol/min/ml) = Dilution /. /. /µ x Sample KA / 14

10 Figure 2. Resorufin standard curve Figure 3. Human myeloid leukemia HL60 10,000 x g supernatant assayed with and without MPO inhibitor. Performance Characteristics Precision When a series of sixteen MPO measurements were performed on the same day, the intra-assay coefficient of variation was 2.8%. When a series of sixteen MPO measurements were performed on five different days under the same experimental conditions, the inter-assay coefficient of variation was 3.12%. KA / 14

11 Assay Range Under the standardized conditions of the assay described in this booklet, the dynamic range of the kit is 0-10 µm of resorufin. Interferences The following reagents were tested in the assay for interference in the assay: Reagent Will Interfere (Yes or No) Buffers Tris No HEPES Yes Phosphate No Detergents Tween 20 (0.1%) Yes Tween 20 (1%) Yes Triton X-100 (0.1%) Yes Triton X-100 (1%) Yes Protease Inhibitors/ EDTA (1 mm) No Chelators/ Enzymes EGTA (1 mm) No Trypsin (10 µg/ml) No PMSF (1 mm) Yes Leupeptin (10 µg/ml) No Antipain (10 µg/ml) No Chymostatin (10 µg/ml) No DSolvents Ethanol (10 µl) No Methanol (10 µl) No Dimethylsulfoxide (10 µl) Yes s BSA (0.1%) Yes Glutathione (1 mm) Yes Glycerol (5%) No KA / 14

12 Resources Trouble shooting Problem Possible Causes Recommended Solutions Erratic values; dispersion of A. Poor pipetting/technique A. Carefully tap the side of the duplicates/triplicates B. Bubble in the well(s) plate with your finger to remove bubbles B. Be careful not to splash the contents of the wells No fluorescence detected in the Sample was too dilute A. Re-assay the sample using a sample wells lower dilution B. Concentrate the sample with an Amicon concentrator with a 30,000 MW cut-off The fluorometer exhibited MAX The GAIN setting is too high A. Reduce the GAIN and values for the wells re-read B. Make sure to establish the GAIN using the resorufin standards before assaying your samples No inhibition was seen with the A. MPO activity is too low to A. Re-assay the sample using a MPO inhibitor detect lower dilution B. The sample does not contain B. Check the interference MPO section for possible C. Sample contains something interfering reagents that is interfering with the assay References 1. Yamada, M. and Kurahashi, K. Regulation of myeloperoxidase gene expression during differentiation of human myeloid leukemia HL-60 cells. J. Biol. Chem. 259(5), (1984). 2. Schultz, J. and Kaminker, K. Myeloperoxidase of the leucocyte of normal human blood. I. Content and localization. Arch. Biochem. Biophys. 96, (1962). 3. Harrison, J.E. and Schultz, J. Studies on the chlorinating activity of myeloperoxidase. J. Biol. Chem. 251(5), (1976). 4. Podrez, E.A., Abu-Soud, H.M., and Hazen, S.L. Myeloperoxidase-generated oxidants and atherosclerosis. Free Radic. Biol. Med. 28(12), (2000). KA / 14

13 5. Zhang, R., Brennan, M.-L., Fu, X., et al. Association between myeloperoxidase levels and risk of coronary artery disease. JAMA 286(17), (2001). 6. Malle, E., Furtmüller, P.G., Sattler, W., et al. Myeloperoxidase: A target for new drug development? Br. J. Pharmacol. 152, (2007). 7. Kettle, A.J., Gedye, C.A., Hampton, M.B., et al. Inhibition of myeloperoxidase by benzoic acid hydrazides. Biochem J. 308, (1995). 8. Kettle, A.J., Gedye, C.A., and Winterbourn, C.C. Mechanism of inactivation of myeloperoxidase by 4-aminobenzoic acid hydrazide. Biochem J. 321, (1997). KA / 14

14 KA / 14 Plate Layout Positive Control Sample Wells Sample + Inhibitor Wells 3 Positive Control Sample Wells Sample + Inhibitor Wells 2 A B C D E F G H 1 A B C D E F G H A B C D E F G H